Characterization of High-Speed Impinging Jets in a High Pressure and Temperature Environment.

The purpose of this work is to study the dense region of two high-speed impinging jets in a temperature and pressure environment that is above atmospheric conditions. The program was terminated one year short due to the departure of the PI from the US. Nevertheless all of the goals that were set for this time period were accomplished. The measurements were performed using a double pulse, two reference beam holographic technique. The working fluids utilized were water, a 59 weight percent aqueous glycerol solution, and ethanol. Velocity measurements and drop-size distributions were obtained for various regions of the spray, and the universal root normal distribution was used as a representation of the cumulative volume distributions. Generally, the qualitative nature of the spray pattern remained the same as temperature increased, however, the size of the resulting droplets decreased as a result of evaporation and increased instabilities. Furthermore, the wave structure, which is characteristic of a fully developed impinging jet spray, became less distinct as temperature increase. Two mechanisms combined to reduce the drop diameters. First, as temperature increases, the viscosity of the air increases and the viscosity of the spray fluid decreases thus, the larger spray structures atomize earlier due to the magnification of aerodynamic instabilities. Second, the heat up of the droplets, which is facilitated by the earlier primary atomization, leads to the evaporation of particle mass, and in the case of the smallest droplets, complete vaporization. Furthermore, the interaction of these two factors causes the representative diameters to increase with temperature over a small range of temperatures beyond the boiling point as the smaller droplets decrease and disappear faster than the larger droplets.